This invention relates to a silent chain including a number of link plates articulately connected together by joint pins and each having a pair of teeth for meshing engagement with sprocket teeth and a pair of pin holes in which the joint pins are inserted.
In general, a silent chain includes articular link rows and guide link rows alternately arranged in the longitudinal direction of the chain and articulately connected by joint pins, such as round pins or rocker joint pins, in such a manner that link plates in each articular link row and link plates in the adjacent guide link row are interleaved in single-to-single, double-to-double, or single-to-double ply bases.
As shown in FIGS. 4 and 5, a conventional silent chain 20 generally comprises link plates 21 and 22 and guide plates 23 (see, Japanese Patent Laid-open Publication No. HEI-11-182635). The plates 21 form articulate link rows KL and, as shown in FIG. 6, the articulate link plate 21 has a hollow cylindrical bushing 26 formed separately from the plate 21 and fitted in each of a pair of engagement holes 25 formed in the plate 21. A joint pin 28 (FIGS. 4 and 5) is inserted into the bushing 26 so that the articulate link plate 21 is rotatable about the axis of the joint pin 28. The plates 22 and the guide plates 23 together form guide link rows GL. The guide link plate 22 has a pair of pin holes (not shown) into which the joint pin 28 is inserted. The guide link plate 22 may be or may not be rotatable about the axis of the joint pin 28. In addition, the guide link plate 22 may or may not have a pair of teeth for meshing engagement with the teeth of a sprocket.
Since the plate 21 is equipped with a bushing 26 fitted in the engagement hole 25, the contact area for sliding engagement between the inside surface of the pin hole 24 and the outside surface of the joint pin 28 is relatively large and hence can suppress wear on the joint pin 28. However, as compared to a bushingless plate 31 such as shown in FIG. 7, a web width W1xe2x80x2 between the outside flank 27A of each tooth 27 and the peripheral edge 25xe2x80x2 of the adjacent engagement hole 25 and a web width W2xe2x80x2 between the inside flank 27B of the same tooth 27 and the peripheral edge 25xe2x80x2 of the adjacent engagement hole 25 are made relatively small provided that the diameter of the pin hole 24 is the same as that of pin holes 32. There arises a problem that the plate 21 cannot maintain the necessary rigidity and strength. Thus, when subjected to a load during meshing engagement between the teeth 27 and the sprocket teeth, the plate 21 is liable to yield or deform due to insufficient rigidity and strength, thus making the meshing engagement unstable.
Most silent chains are formed solely by bushingless plates 31, namely, plates not quipped with a bushing. As shown in FIG. 7, the bushingless plate 31 can provide a relatively large web width W1, W2 between the peripheral edge 32xe2x80x2 of each pin hole 32 and the outer or inner flank 33A or 33B of the adjacent tooth 33. Accordingly, even if the thickness of the plate 21 is reduced, the plate 21 is still able to maintain the necessary rigidity and strength. However, since the contact area for sliding movement between the inside surface of the pin hole 32 and the outside surface of the joint pin 28 decreases with the reduction in thickness of the plate 21, wear elongation of the silent chain is caused due to accelerated wear on the joint pin 28. To deal with this problem, the thickness txe2x80x2 of the plate 31 is increased to enlarge the contact area between the pin hole 32 and the joint pin 28, as shown in FIG. 8. However, the plate 31 becomes heavy and the overall weight of the silent chain is increased.
It is accordingly an object of the present invention to provide a silent chain which is capable of providing a relatively large contact area between pin holes in the link plates and joint pins without narrowing the web width between each pin hole and the outside or inside flank of the adjacent tooth of the link plate, thereby to suppress wear on the joint pins, prevent reduction in strength of the link plate, and limit the increase in the overall weight of the silent chain.
To achieve the foregoing object, a silent chain according to the present invention comprises a number of interleaved rows of link plates articulately connected together by joint pins. Each of the link plates has a pair of teeth and a pair of pin holes. The link plate has a tubular portion protruding continuously from one surface of the link plate and defining a peripheral surface of each of the pin holes. The tubular portion has a height substantially equal to the thickness of the link plate.
In each row of link plates, two link plates may arranged side by side with the respective tubular portions oriented in the same direction.
Alternatively, in each row of link plates, two link plates may be arranged side by side with the respective tubular portions oriented in the opposite directions. The tubular portions of one of the link plates and the tubular portions of the other link plate may be directed toward each other or directed away from each other.
The tubular projection is preferably formed by burring.
By virtue of the tubular portion, the link plate can retain a relatively large contact area between itself and joint pins and hence is able to suppress wear on the joint pins. In addition, the web width between each pin hole and the outside flank or the inside flank of the corresponding tooth is enlarged with the result that the link plate is highly resistant to deformation or yielding when it comes into meshing engagement with the sprocket teeth.
The above and other objects, features and advantages of the present invention will become manifest to those versed in the art upon making reference to the following description and accompanying sheets of drawings, in which certain preferred structural embodiments incorporating the principle of the invention are shown by way of illustrative example.